1. Field of the Invention
The present invention relates to a thermally-assisted magnetic write head used in thermally-assisted magnetic writing in which near-field light is applied to a magnetic recording medium to lower a coercivity thereof so as to record information, and to a head gimbal assembly, a head arm assembly, and a magnetic disk unit that are mounted with the thermally-assisted magnetic write head.
2. Description of Related Art
In the past, a magnetic disk unit has been used for writing and reading magnetic information (hereinafter, simply referred to as information). The magnetic disk unit includes, in the housing thereof for example, a magnetic disk in which information is stored, and a magnetic read write head that records information into the magnetic disk and reproduces information stored in the magnetic disk. The magnetic disk is supported by a rotary shaft of a spindle motor, which is fixed to the housing, and rotates around the rotary shaft. On the other hand, the magnetic read write head is formed on a side surface of a magnetic head slider provided on one end of a suspension, and includes a magnetic write element and a magnetic read element that have an air bearing surface (ABS) facing the magnetic disk. In particular, as the magnetic read element, an MR element exhibiting magnetoresistive effect (MR) is generally used. The other end of the suspension is attached to an end of an arm pivotally supported by a fixed shaft installed upright in the housing.
When the magnetic disk unit is not operated, namely, when the magnetic disk does not rotate and remains stationary, the magnetic read write head is not located over the magnetic disk and is pulled off to the outside (unload state). When the magnetic disk unit is driven and the magnetic disk starts to rotate, the magnetic read write head is changed to a state where the magnetic read write head is moved to a predetermined position over the magnetic disk together with the suspension (load state). When the rotation number of the magnetic disk reaches a predetermined number, the magnetic head slider is stabilized in a state of slightly floating over the surface of the magnetic disk due to the balance of positive pressure and negative pressure, and thus, information is accurately recorded and reproduced.
In recent years, along with a progress in higher recording density (higher capacity) of the magnetic disk, improvement in performance of the magnetic read write head and the magnetic disk has been demanded. The magnetic disk is a discontinuous medium including collected magnetic microparticles, and each magnetic microparticle has a single-domain structure. In the magnetic disk, one recording bit is configured of a plurality of magnetic microparticles. Since the asperity of a boundary between adjacent recording bits is necessary to be small in order to increase the recording density, the magnetic microparticles are necessary to be made small. However, if the magnetic microparticles are made small in size, thermal stability of the magnetization of the magnetic microparticles is disadvantageously lowered with decreasing volume of the magnetic microparticles. To solve the issue, increasing anisotropy energy of the magnetic microparticle is effective. However, increasing the anisotropy energy of the magnetic microparticle leads to increase in the coercivity of the magnetic disk, and as a result, difficulty occurs in the information recording in the existing magnetic head.
As a method to solve the above-described difficulty, a so-called thermally-assisted magnetic writing has been proposed. In the method, a magnetic recording medium with large coercivity is used, and when information is written, heat is applied together with the magnetic field to a section of the magnetic recording medium where the information is to be written to increase the temperature and to lower the coercivity of that section, thereby writing the information. Hereinafter, the magnetic head used in the thermally-assisted magnetic writing is referred to as a thermally-assisted magnetic write head.
In performing the thermally-assisted magnetic writing, near-field light is generally used for applying heat to a magnetic recording medium. For example, in Japanese Unexamined Patent Application Publication No. 2001-255254 and in Japanese Patent No. 4032689, disclosed is a technology of allowing frequency of light to coincide with a resonant frequency of plasmons that are generated in a metal, by directly applying the light to a plasmon generator, in order to generate near-field light. In the method of directly applying light to a plasmon generator, however, the plasmon generator itself overheats and accordingly deforms, depending on usage environment or conditions. Therefore, practical realization of the method is difficult.
Therefore, as a technology capable of avoiding such overheating, in Japanese Patent No. 4104584, a thermally-assisted head using surface plasmon polariton coupling is proposed. In this technology, without direct irradiation of light propagating through a waveguide (guided light) to a plasmon generator, the guided light is coupled to the plasmon generator through evanescent coupling, and surface plasmon polaritons generated on a surface of the plasmon generator are used.
In the thermally-assisted writing technology, it is important to generate light spots with a fine diameter. This is because, on the magnetic recording medium, a region (heat spot) heated to a temperature equal to or greater than the Curie temperature Tc is reduced in size as much as possible so that magnetic information recording with higher density is achieved.
Along with reduction of the heat spot, however, recording point in which magnetic recording is actually performed on the magnetic recording medium is away from a magnetic pole that generates a recording magnetic field. This is because the plasmon generator and the magnetic pole are different components arranged adjacent to each other along the air bearing surface, and therefore, generation position of the near-field light is away from the generation point of the recording magnetic field to some extent.
Generally, the recording magnetic field from the magnetic pole toward the magnetic recording medium has high intensity in a region of the magnetic recording medium facing the magnetic pole, and is decreased in intensity with increase in distance from the magnetic pole. Therefore, if the heat spot is made too small, intensity of the recording magnetic field necessary for magnetic recording in a recording point where recording operation should be performed is not obtained. In addition, even if the recording operation is possible, when the recorded region in which desired magnetic information has been written passes through the region facing the magnetic pole, unintentional overwriting may be performed due to an applied recording magnetic field with higher intensity.
Accordingly, it is desirable to provide a thermally-assisted magnetic write head capable of performing accurate recording operation without unintentional overwriting, as well as performing magnetic recording with higher density.